1. Field of the Invention
The present invention relates generally to methods and apparatuses for extracting heat from combustible materials, and, more particularly, to a method and apparatus for combusting a solid material strip at a controlled temperature.
2. Description of the Prior Art
Historically, solid fuel was burnt mainly by the flatbed combustion process. In the past two decades, solid fuel was replaced by liquid fuel, because liquid was less labor intensive and was cleaner in operation. The liquid fuel was burnt by spraying the liquid fuel through a high-speed nozzle to atomize the fuel. In recent years, as liquid fuel became more costly, many power plants were modified for both liquid and powdered solid fuel combustion using the spraying technique originally designed for the liquid fuel. For home heating, liquid fuel is still in wide use, mainly due to the handling and pollution problems of solid fuel.
The fundamental problem with both liquid and powdered solid fuel combustion is that both types of combustion are unstable runaway forms of combustion which generally take place within 10 milliseconds, since it is nearly impossible to control the reaction rates inherent in these types of combustions. The resultant high temperatures of combustion promote excessive production of carbon monoxide, nitrogen oxides, and sulfur oxides, and the production of corrosive and coating micro flyash. These byproducts of combustion are the cause of many environmental and operational problems, i.e. the pollution of the atmosphere and the coating of heat exchangers resulting in reduced heat exchange efficiency, whose avoidance greatly increases the cost of combusting liquid and powdered solid fuels.
Also, the processes used in the prior art combustion methods often result in combustion temperatures of over 2000.degree. C. At such a high temperature the combustion product is mainly CO instead of CO.sub.2. Consequently, a large power plant requires a mammoth combustion chamber to provide sufficient resident time for the CO gas to complete a secondary combustion into CO.sub.2 at a lower temperature of about 1000.degree. C., thus increasing the cost of operating the power plant. It is clear that a form of combustion is needed which avoids these problems.